On 7/16/21 10:12 PM, Linus Torvalds wrote: > On Fri, Jul 16, 2021 at 12:39 AM Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: >> >> This somewhat unexpectedly causes a crash when running the xfs/433 test >> in xfstests for me. Reverting the commit fixes the problem: > > I don't see why that would be the case, but I'm inclined to revert > that commit for another reason: the code doesn't seem to match the > description of the commit. > > It used to be that CONFIG_SLUB_DEBUG was a config option that was > harmless and that defaulted to 'y' because there was little downside. > In fact, it's not just "default y", it doesn't even *ask* the user > unless CONFIG_EXPERT is on. Because it was fairly harmless. And then > SLOB_DEBUG_ON was that "do you actually want this code _enabled_". > > But now it basically force-enables that STACKDEPOT support too, and > then instead of having an _optional_ CONFIG_STACKTRACE, you basically > have that as being forced on you whether you want active debugging or > not. > > Maybe that > > select STACKDEPOT if STACKTRACE_SUPPORT > > should have been > > select STACKDEPOT if STACKTRACE I recall we tried that and run into KConfig recursive dependency hell as "config STACKDEPOT" does "select STACKTRACE", and after some attempts ended up with the above. > because i\t used to be that CONFIG_STACKTRACE was somewhat unusual, > and only enabled for special debug cases (admittedly "CONFIG_TRACING" > likely meant that it was fairly widely enabled). > > In contrast, STACKTRACE_SUPPORT is basically "this architecture supports it". > > So now it seems STACKDEPOT is enabled basically unconditionally. It seemed rather harmless as it was just a bit of extra code. But it's true Geert reports [1] unexpected memory usage which I would have only expected if actual stacks started to be collected. So I guess we'll have to look into that. [1] https://lore.kernel.org/lkml/CAMuHMdW=eoVzM1Re5FVoEN87nKfiLmM2+Ah7eNu2KXEhCvbZyA@xxxxxxxxxxxxxx/ > So I really don't see why it would cause that xfs issue, but I think > there are multiple reasons to just go "Hmm" on that commit. > > Comments? > > Linus >
